题目1：

主程序：

package test;

import java.util.Scanner;

public class Rectangle {
    public static void main(String[] args) {
        Scanner s = new Scanner(System.in);
        System.out.println("请输入长宽高:");
        double s1 = s.nextDouble();
        double s2 = s.nextDouble();
        double s3 = s.nextDouble();
        Rectangletest sc = new Rectangletest(s1, s2);
        Cuboid cb = new Cuboid(s1, s2, s3);
        System.out.println("周长:" + sc.perimeter() + "面积:" + sc.area() + "体积为:" + cb.volume() + "表面积:" + cb.allarea());
    }
}

父类：

package test;

public class Rectangletest {
    private double length;
    private double width;

    public Rectangletest() {
        this(0.0, 0.0);
    }

    public Rectangletest(double length, double width) {
        this.length = length;
        this.width = width;
    }

    double perimeter() {
        double p = (this.width + this.length) * 2;
        return p;
    }

    double area() {
        double a = this.width * this.length;
        return a;
    }

    public double getlength() {
        return length;
    }

    public double getwidth() {
        return width;
    }

}

子类：

package test;

public class Cuboid extends Rectangletest {
    double height;

    public Cuboid() {
        this(0, 0, 0);
    }

    public Cuboid(double length, double width, double heigth) {
        super(length, width);
        this.height = heigth;
    }

    public double allarea() {
        double ar = ((super.getlength() * super.getwidth()) + (super.getlength() * height)
                + (super.getwidth() * height)) * 2;
        return ar;
    }

    public double volume() {
        return super.area() * height;
    }

}

附带源代码：

题目2：

package com;

public class A {
    public int a = 1;
    private int b = 2;
    protected int c = 3;
    int d = 4;

    public int getA() {
        return a;
    }

    public void setA(int a) {
        this.a = a;
    }

    public int getB() {
        return b;
    }

    public void setB(int b) {
        this.b = b;
    }

    public int getC() {
        return c;
    }

    public void setC(int c) {
        this.c = c;
    }

    public int getD() {
        return d;
    }

    public void setD(int d) {
        this.d = d;
    }
}

package com;

public class B extends A {

    public static void main(String[] args) {
        B b1 = new B();
        System.out.println(b1.a);
        // System.out.println(b1.b); //同包不同类，私有不可访问
        System.out.println(b1.c);
        System.out.println(b1.d);
    }
}

package com;

public class C {

    public static void main(String[] args) {
        A a1 = new A();
        System.out.println(a1.a);
        // System.out.println(a1.b);//同包不同类，私有不可访问
        System.out.println(a1.c);
        System.out.println(a1.d);
    }
}

——————————————–以上为com包—————————————

package org;

import com.A;

public class D {

    public static void main(String[] args) {
        A d1 = new A();
        System.out.println(d1.a);
        // System.out.println(d1.b);//不同包，除共有外均不可直接访问
        // System.out.println(d1.c);
        // System.out.println(d1.d);
    }
}

package org;

import com.A;

public class E extends A {

    public static void main(String[] args) {
        E e1 = new E();
        System.out.println(e1.a);
        // System.out.println(e1.b); //不同包，继承私有不可访问，但可get，如下；
        System.out.println(e1.getB());
        System.out.println(e1.c);
        // System.out.println(e1.d);//不同包，继承缺省不可访问，但可get，如下；
        System.out.println(e1.getD());
    }
}

——————————————–以上为org包—————————————

源码：

题目3：

package castDemo1;

class Employee {
}

class Manager extends Employee {
    public String toString() {
        return "i'm a manager.";
    }
}

public class CastDemo1 {

    public static void main(String[] args) {
        Employee stuff;
        Manager boss = new Manager();
        stuff = boss;
        Manager myBoss;
        myBoss = (Manager) stuff;
        System.out.println(myBoss);
    }
}

源码：

题目4：

package EdibleTest;

interface Ediable {
    public abstract String howToEat();
}

abstract class Food {
}

abstract class Fruit extends Food implements Ediable {
}

class Beef extends Food implements Ediable {
    public String howToEat() {
        return "Fried Beef Steak";
    }
}

class Mutton extends Food implements Ediable {
    public String howToEat() {
        return "Roast Mutton";
    }

}

class Apple extends Fruit {
    public String howToEat() {
        return "Make Apple Pie";
    }
}

class Orange extends Fruit {

    public String howToEat() {
        return "Make Orange Juice";
    }
}

public class EdibleTest {

    public static void main(String args[]) {

        Object[] obj = { new Beef(), new Mutton(), new Apple(), new Orange() };
        for (int i = 0; i < obj.length; i++) {
            if (obj[i] instanceof Ediable)
                System.out.println(((Ediable) (obj[i])).howToEat());

        }
    }
}

 源码：